[client] initialize markings to None instead of [] (opencti #12095)

[JeremyCloarec]

Proposed changes

• extracted object markings were initialized to [] instead of None, causing ingestion to not apply default values

Related issues

• Default marking not applied opencti#12095

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...